Conventionally, when character information is extracted from a document, the document is read using a scanner or the like to generate a digital image. Such a digital image generated from a document in this manner may contain noise. To remove the noise contained in the digital image, it is possible to use a noise removal filter such as a median filter, average filter, Gaussian filter, or the like.
There is known a method for S/N (Signal/Noise) ratio dependent image processing, as a related art. The image processing method includes computing at least one S/N ratio for at least one region of an image, determining a filter parameter based on the at least one S/N ratio, and processes the at least one region of the image based on the filter parameter.
As another related art, there is known an image signal processing device including an area dividing unit that divides image signals acquired by an image capturing element and subjected to predetermined image processing into a plurality of areas on the basis of color information and a noise reducing unit that performs different noise reduction processing on the individual areas of the image signals divided by the area dividing unit.
Related art is disclosed in U.S. Pat. No. 7,248,749 and U.S. patent application publication No. 2010/0182461.